Re: [HACKERS] UPDATE of partition key - Mailing list pgsql-hackers

On Fri, Mar 17, 2017 at 4:07 PM, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
> On 4 March 2017 at 12:49, Robert Haas <robertmhaas@gmail.com> wrote:
>> On Thu, Mar 2, 2017 at 11:53 AM, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
>>> I think it does not make sense running after row triggers in case of
>>> row-movement. There is no update happened on that leaf partition. This
>>> reasoning can also apply to BR update triggers. But the reasons for
>>> having a BR trigger and AR triggers are quite different. Generally, a
>>> user needs to do some modifications to the row before getting the
>>> final NEW row into the database, and hence [s]he defines a BR trigger
>>> for that. And we can't just silently skip this step only because the
>>> final row went into some other partition; in fact the row-movement
>>> itself might depend on what the BR trigger did with the row. Whereas,
>>> AR triggers are typically written for doing some other operation once
>>> it is made sure the row is actually updated. In case of row-movement,
>>> it is not actually updated.
>>
>> How about running the BR update triggers for the old partition and the
>> AR update triggers for the new partition?  It seems weird to run BR
>> update triggers but not AR update triggers.  Another option would be
>> to run BR and AR delete triggers and then BR and AR insert triggers,
>> emphasizing the choice to treat this update as a delete + insert, but
>> (as Amit Kh. pointed out to me when we were in a room together this
>> week) that precludes using the BEFORE trigger to modify the row.
>>

I also find the current behavior with respect to triggers quite odd.
The two points that appears odd are (a) Executing both before row
update and delete triggers on original partition sounds quite odd. (b)
It seems inconsistent to consider behavior for row and statement
triggers differently

>
> I checked the trigger behaviour in case of UPSERT. Here, when there is
> conflict found, ExecOnConflictUpdate() is called, and then the
> function returns immediately, which means AR INSERT trigger will not
> fire. And ExecOnConflictUpdate() calls ExecUpdate(), which means BR
> and AR UPDATE triggers will be fired. So in short, when an INSERT
> becomes an UPDATE, BR INSERT triggers do fire, but then the BR UPDATE
> and AR UPDATE also get fired. On the same lines, it makes sense in
> case of UPDATE=>DELETE+INSERT operation to fire a BR UPDATE trigger on
> the original table, and then the BR and AR DELETE/INSERT triggers on
> the respective tables.
>

I am not sure if it is good idea to compare it with "Insert On
Conflict Do Update", but  even if we want that way, I think Insert On
Conflict is consistent in statement level triggers which means it will
fire both Insert and Update statement level triggres (as per below
note in docs) whereas the documentation in the patch indicates that
this patch will only fire Update statement level triggers which is
odd.

Note in docs about Insert On Conflict
"Note that with an INSERT with an ON CONFLICT DO UPDATE clause, both
INSERT and UPDATE statement level trigger will be fired.



-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com